Push-pull amplifier circuit



April 18, 1933. F. THoRlNGToN PUSH-PULL AMPLIFIER CIRCUIT Filed Nov. l5, 1929 NNN.

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l outputgreater than that' which would be available from asingle"v tube in the power qui-res no external fieldsupply for the loud Patented Apr. 178, 19733 FLETCHER. 'rHoRIISTer'0N;v or BIRMINGHAM, aLABAMn- A; 'PUSILPULL AMrLIrIEn *omcrrfj` 'f an amplifier circuit which hasan undistortedA Another object `of the invention is to design a' push-pull amplifier circuit which respeaker?.

A11further object. lof the 'invention is to Y providefa push-pull circuit'which will perf mit the power tubes to'operate'at full capac-rV i itywithout distortion.

YAnd Va still-further'object'ofztheinvention K Y nected in seriesgand to :the grids 20 and 24 Y is to provide a circuit `arrangement which will; permit thecontrol of the low frequency together with the high frequency for adjustdesiredrconditions.

Y ing. the tone quality of the instrument to any In carryin'gfmy inventionii-nto .eecttheinputfroin the phone pick up or radiois u connected-to Atwo audio transformers having their primaries connected. in parallel and t their?.secondariesfini series.- A 250,000 ohm resistorr'isrshunted across the secondaries of eachftrans'former. The secondary terminals of theA input transformers are connectedto the gridsof thefirst stage tubes .which are connecteclin push-pull. The second stage tubes which are likewise in pushl'pull ar; rangement are coupledy to the first stage by two transformers eachV having their primaries andV secondaries ,connected in series' 'and ibeing'ofthe-sameA type as the first stage trans` y ferrners.1' The 4primaries'- and secondares of eachtransformer ofthe: second stage are -4e connected in seriesy and to the output circuit off' theiirst stage. Thesecondaries'are' con-I nectedto the grids or'` input circuit ofthe second stage".A The output circuit of the second stage is connected to an output trans! formerwith tapped secondary winding. to properly inatc'hthe impedance of different speakers to theoutput of the amplifier. A plurality of small capacity con'dens'ers are connected across the grids of the first stage.V

`Similar condensers are also connectediny series with the-secondary. circuit of the-output` transformer and the Voice. coils.x.'- o, Y A

Th features ofmy invention which I conf` sider nevel .are ypointed'"outwithxparticu larity inthe' appended claimsThe. invene tion itself,however, both-as toits arranger-5 ment and. method of operation together with further objects and advantages thereofjwill be besty understood-by reference 'tosthe fols lowing description taken in connectionfwith the *accompanying drawing Awhich is'axdia; grammatic representation of the connections;

The input is connected by the conductors f connected in- `parallel."` The secondaries r 10 and 12 of the'iirst stage -transforrnerfare con-fk y250,000 ohms are "shunted across` eachaof the `2 and 4i tothe primaries 6i and,'Siti/hich:` are secondaries'l() and 12. .l Agvariable capacity condenser 28 'consisting of r,a f plurality of small capacity condensersiis Sllllltedwacfress Y the grids andV 24.' y This'peimjts gxtremly high flqllcncie'sfto be cut down Vto any dei sired level." Y

ranged in push-pull have their grids :.350V andl 32 coupled with' thegplates 34`and 36Vof the first stagetubesV by means of a pair of-l transe foi-mersY ofthe type as'used in the'frstjstage. The primaries 38 and'40 of-,each second stage transformer are connected ,respectively .in

y series with ,their secondaries 42 and V44 jby Y means of external jumpers 46 andg- 48. The' primaries 38 and 4Oare-` connected infseries The secondlstage" tubes. Y

and 'thev plates V34 and 36 .of the --iirst'fstfiggge?,

tubesfare connected by lmeans offc'onductors 50 and 52;.through condensers 54and` 581@ the primaries 38 and l0-at the pointof enternal .connectionbetween the primary and. sec,- ondary windings of the transformers' Sec;

` ondaries 42 and 44 are each respectively con..-

nectedY to grids SOand 32 of thesecondlstage tubes byconductors 'and .62. Y

Two'subsanaauy100,000hmfesiaof164 and k68 Y are` connected in series and across the y plates34 andV 36 ofy the firststage tubesi l .y The Voltage change across/these resistors causes a corresponding signal to be transmitted to the second stage transformers which act as an auto transformer with a high step up ratio of amplification. Resistors 70 vand 74 of substantially 100,000 ohms are connected respectively across the primary and secondary of 'each of the secondV stage transformers in order to stabilize the amplier and?4 improve. .the tone quality. The plates 76 and 78 ofthe second stage tubes are Connectedrby means of conductors 80 and 82;'toth-e Vprimarywindings 84 and 86, respectively, of the output transformer. The secondary windingsv 88, 90, 92 and 94 of the outputv transformer areconnected to match the impedance of the number of speakers used. The secondaries of the output transformer` are connected toa loud speaker or' thelikeby,v means of conductors 96 'and 98 in series witha variable capacity-.condenseii -100 which consistsvoff a plurality of small capaci-ty condensers.,.` 'Ihe variable capacitycondenser 100 whichi's connectedin vseries with-the voice coils. of a dynamicv speaker permits thecontrolling of the lower :frequencies andenables the operator to prevent` theV lower bass notes from entering rthefliorn and A'causing adeepj'barrel tone sound. Y f. l "It is `obvious thatthe amplifier may be supplied with Valternating or direct current.

*Howevergin' thei drawing, y analternating current source offsupply is utilizedf An alternating current', source Vof'supplyyis connected to the primary 102 of the powertransformer 104. The powertransformer 104 has a plurality of secondary windings. Secondary-hwindin'gsv 106 and -`108 are'connected inl series fand' to plates v110% and 112 .ofy the itwol recti-fierft'ub'es; :1A :conduct'or-j114 connects the"windingsl .through choke" `coils 116 and 118 tothel center taps of the filaments. These Y choke coilsinay consist of from one'to four of-the field Vcoils vof a dynamic speaker unit or units, ,Secondaryjwindin'gs 120 supply thelilarnents122 andv 124 4of the first stage tubes withfcurrent'through conductors 126 andf128. l Filaments130'and132of the powertubes'of the second stage are`1'supplied with current from the Ysecondary windings .134of the power transformer through leads 13,6 and 138.V Thefresistances-let and 142 ar'eiconnected together 7by'ineans of a. coin'- 'ductor'1441which is connected tothe negative Bf source of @supply through Yconductor 1141" Y *5 i f V Filaments 146'and148'-v4 of the "rectifier tubes are connected to'fthe Vsecondary winding 150 of the power transformery 104".y Secondary winding 150 atits midpoint is conn nected by means .ofconductor 152 to the plate circuit ofthe first-stage tubes'at vthe midpoint yof the connection of resistors 64 andv 68 which arejconnected across the plates 34 Vand 36.` Conductor 154 which is connectedto the conductor 152 is connected at the midpoint of the output transformer `and supplies the plates 7 6 and 7 8 of the second vtotli'egrids 20 and 24'ofthe first stage tubes by conductorl 166and the negative 84 volt C bias is connected to the grids 30 and 32 of tliefsecond stagetubes by conductor 168.

This amplifier while of avery simple and compactfdesign requiresl no external field supply for the speaker units and operates the second stage Apower tubes in"pushpull arrangement at a-very high capacity with-l out distortion".A While I have described my invention 'with particular reference to; the* two stage amplication circuit, Ido not;

wish to bel liniited 'tothe' use Iof the particular circuit connections shown and described,

as'it will be apparent thatmy system may be utilizedin other manners to advantage for amplificationand that :many modifications .in the connectionsused may `beniade. without departing from the scopeof my inveiition as set forth inthe appendedfclaims.

-What I claim as new and desire .to secure by Letters Patent of the-United kStates is:

1. In atwo stage cascade amplifiercircuit, a pair of transformers in said' firstV vstage having their primary windings connected in reverse parallel and their Vsecondary windings" connected in series, y high. :resistances connectedfin shuntewitrihA each of ysaid* secondary windingsa pair: of transformersin the-second stage having the secondary windings of'each'transformer connected-in series andl the primary: windings-off'eacli;transfy former connectedin series andtothefoutput .y

circuit of the first stage tubes, a pair lof high resistances connected' inseries and across the output circuit o f saidl firststagetubes and :high resistances connected across the windings of each of said second stage transformers.\ Y Y v f. 2.7Atwo-stage cascade amplifying circuit comprising a pair of v transformers? having theirfpiimaries connectedinyreverse par"- allel and their secondaries in series,said primariesbeing adapted to beconnected to an inputcircuit, a pair of power tubes having their, grids connected to thesecondaries of said transformers, highrresistances. shunted across each of the :secondaries ofv saidtrans.- former, a variable capacitycondenserconc sisting of a plurality of small capacity condensers connected in` shunt with said'sec'ondariesof said transformers; as econd pair of transformers each .j having .theirv ,windings connected .in series, said primary'windings of: fsaid'"transformers 'being connected in series and to the plate circuits of said pair of power tubes, condensers connected in circuit with said plates and said primary windings of said transformers, a pair ofkhigh resistances connected across Ythe plates of said tubes, resistances connected across the windings of each of said second pair of transformers, a second pair of tubes, the grids of said second pair of tubes being connected to the secondary windings of said second transformer, an output transformer having its primary winding connected to the output circuit of said second pair of tubes, the secondary winding of said output transformer having a plurality of windings, a variable capacity condenser consisting of a plurality of small capacity condensers connected in series with said secondary windings of said output transformer, and means connected to said amplifier circuit for supplying it with power.

In testimony whereof I affix my signature.

FLETCHER THORINGTON. 

